1. Field of the Invention
The present invention relates to an image pickup apparatus in which normal transfer of signal electric charges for a read operation and high-speed sweep transfer for a purge operation of useless electric charges are performed for a solid state image pickup device, and more particularly to an image pickup apparatus which can reduce a circuit scale.
2. Description of the Related Art
Hitherto, there is known an image pickup apparatus which includes a CCD image pickup device designed to perform normal transfer of signal electric charges for a read operation and high-speed sweep transfer for a purge operation of useless electric charges, and which is constructed as shown in FIG. 1. The illustrated construction shows an electronic camera using a CCD image pickup device. In FIG. 1, denoted by reference numeral 1 is a lens, 2 is a CCD image pickup device, 3 is a signal processing circuit for processing an output signal of the CCD image pickup device 2 to form an image signal, 4 is a recording unit for recording the image signal from the signal processing circuit 3, 5 is a signal generator for outputting drive signals, etc. to the components, 6 is a CPU for driving and controlling the components, and 7 is a release mechanism unit (including a record trigger for starting a recording operation) which is operated by an operator (photographer) for recording.
As one exemplified construction of the CCD image pickup device 2 shown in FIG. 1, FIG. 2 shows a general construction of a CCD image pickup device 2 of vertical overflow drain/interline type. In FIG. 2, denoted by 11 is a photodiode constituting each of pixels which are arrayed two-dimensionally, and 12 is a transfer gate area for transferring signal electric charges accumulated in the photodiode 11 to a vertical shift register 13. The signal electric charges transferred to the vertical shift register 13 are then transferred to a horizontal shift register 14. The signal electric charges transferred to the horizontal shift register 14 are further transferred therein and delivered to an output terminal through a signal detector 15.
The operation of the image pickup apparatus thus constructed will now be described with reference to a timing chart shown in FIG. 3. In FIG. 3, VD represents a vertical synchronizing signal and HD represents a horizontal, synchronizing signal. Respective frame periods VD1, VD2, VD3, VD4 and VD5 are each set by the vertical synchronizing signal VD. FIG. 3 shows the case where the record trigger for starting the recording operation is output in the frame period VD2. VSUB represents a pulse for purging out signal electric charges, which are accumulated in each photodiode of the CCD image pickup device, to the substrate side, i.e., a timing pulse for determining an exposure period of the CCD image pickup device. In the timing chart of VSUB, periods t1, t2, t3 and t4 each represent the exposure period during which electric charges are generated upon light entering the photodiode of the CCD image pickup device and accumulated therein, and hence during which VSUB is not output. The signal electric charges accumulated in the photodiode are transferred to the vertical shift register by a transfer pulse TG. Transfer pulses TG1, TG2, TG3 and TG4 are output respectively for each of the frame periods VD1, VD2, VD3 and VD4. The signal electric charges transferred to the vertical shift register are then transferred successively by vertical transfer pulses V1, V2, V3 and V4 in four phases to the horizontal shift register. CLP represents a clamp pulse for stabilizing the image signal from the DC point of view. The clamp pulse CLP clamps a CCD signal output from the CCD image pickup device, thereby enabling the stable image signal to be supplied.
As shown in the timing chart of FIG. 3, when the record trigger is output during the frame period VD2 to start the recording operation, an operation of discarding the electric charges, which are accumulated due to the exposure during the exposure period t2 within the frame period VD2, as useless electric charges is first carried out. This useless charge purging operation is performed in a period t corresponding to the frame period VD3 by a high-speed sweep using the vertical transfer pulses V1, V2, V3 and V4. The reason why the high-speed sweep should be effected is as follows. When making exposure within the frame period VD3, if the signal electric charges accumulated in the exposure period within the preceding frame period VD2, a phenomenon called smear occurs and a normal image cannot be obtained. Practically, in the case of photographing an object of high brightness, the signal electric charges accumulated during the frame period VD2 remain in the transfer line and are added to the signal electric charges generated due to the exposure within the frame period VD3, the resulting increased charges being output to as an CCD signal CCD3. To overcome such a problem, the above high-speed sweep operation must be performed so that the signal electric charges accumulated during the exposure period within the frame period VD2 are all discarded out of a CCD output unit.
The frame period VD3 in which the above high-speed sweep operation is performed is also an image pickup period requested by the record trigger, within which the photodiode of the CCD image pickup device is subjected to exposure during the exposure period t2 and electric charges are accumulated in the photodiode. In the frame period VD4, the electric charges accumulated in the respective photodiodes are sequentially output as the CCD signal in the form of CCD3. Incidentally, the CCD signal has optical black areas tob1 and tob2 positioned at the head and tail, respectively, for determining a black level and an intermediate area tO provides an actual effective frame area.
FIGS. 4A and 4B are timing charts for explaining the transfer timing for the normal read operation from the vertical shift register and the high-speed purging operation for purging out the useless electric charges transferred to the vertical shift register, respectively, in the above-described conventional image pickup apparatus. As shown in FIG. 4A, the transfer timing for the normal read operation is set by generating the vertical transfer pulses V1, V2, V3 and V4 in synchronism with the horizontal synch signal HD. On the other hand, FIG. 4B shows the timing at which the vertical transfer pulses are generated for purging out the useless electric charges at a high speed. In the high-speed sweep operation, the vertical transfer pulses are generated successively, as shown, so that the electric charges are swept away. Thus, the transfer operation for normal reading of the accumulated electric charges and the transfer operation for purging out the useless electric charges are different from each other in nature. In the conventional image pickup apparatus, therefore, transfer pulses are formed by separate circuits and supplied to the vertical shift register of the CCD image pickup device in a switching manner between the two transfer operations. However, forming the vertical transfer pulses for the normal read operation and the high-speed sweep operation by separate circuits raises the problem of increasing a circuit scale.
Also, when the vertical transfer pulses are generated at a certain pulse cycle successively for the high-speed sweep operation, there may occur a mismatch in timed relation between the vertical transfer pulses and the horizontal synchronizing signal HD within one horizontal period, as shown in FIG. 4B; hence a vertical transfer stop period tv may occur. This raises the problem that the timing of the vertical transfer pulses cannot be managed within each horizontal period and a circuit scale is necessarily increased because of a difficulty in timing control.
Further, in the conventional image pickup apparatus, the operation for sweeping away the useless electric charges is performed in units of one vertical period. Such a conventional scheme of performing the high-speed sweep operation in units of one vertical period, however, prolongs the sweep period and increases the number of times of the vertical transfer pulses V1-V4 being applied at a full level. Thus, there arises another problem that an amount of electric power consumed is increased correspondingly.
Additionally, in the conventional image pickup apparatus, the clamp pulse CLP is output to clamp the CCD signal continuously including the period of high-speed sweep operation, as shown in the timing chart of FIG. 3. This raises the problem that the swept signal electric charges are mixed in the optical black areas of the output CCD signal and a stable image cannot be obtained.
The present invention has been made with a view of solving the above-mentioned problems in the conventional image pickup apparatus, and a main object of the present invention is to provide an image pickup apparatus in which a circuit for generating vertical transfer pulses (control pulses) for the normal read operation and a circuit for generating vertical transfer pulses (control pulses) for the high-speed sweep operation are used in common and hence a circuit scale is reduced.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical shift register for receiving signal electric charges of each photoelectric transducer and transferring the signal electric charges in the vertical direction, and a horizontal shift register for transferring the signal electric charges in the vertical shift register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in a mode for sequentially transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, and a driving function in a mode for continuously transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register, the control means applying control pulses for driving the vertical shift register to the solid state image pickup device, the timing of the control pulses being set to be substantially the same in the two modes.
By setting the timing of control pulses (vertical transfer pulses) for driving the vertical shift register to be substantially the same in both a normal signal-charge read mode for sequentially transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, and a high-speed sweep mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register, there can be provided an image pickup apparatus in which the control pulses for use in both the modes can be formed by a common circuit and the circuit configuration can be simplified.
Another object of the present invention is to provide an image pickup apparatus which can manage the timing of the vertical transfer pulses just within one horizontal period, can make the timing control easy, and can reduce a circuit scale.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical shift register for receiving signal electric charges of each photoelectric transducer and transferring the signal electric charges in the vertical direction, and a horizontal shift register for transferring the signal electric charges in the vertical shift register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in a mode for sequentially transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, and a driving function in a mode for continuously transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register, the control means applying control pulses for driving the vertical shift register to the solid state image pickup device, and a pulse cycle W of the control pulses applied in the mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register is set to meet the relationship of 1H=Wxc3x97n (n is one or more integer) for one horizontal period (1H) in the mode for sequentially transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register in synchronism with the transfer operation of the horizontal shift register.
By setting the pulse cycle W of the control pulses (vertical transfer pulses) for driving the vertical shift register, which are applied in a high-speed sweep mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register, so as to meet the above relationship, it is possible to avoid a mismatch between the control pulses and a horizontal synchronizing signal HD within one horizontal period. There can be thus provided an image pickup apparatus in which the timing of the control pulses can be managed just within one horizontal period, the timing control can be made easy, and the circuit scale can be reduced.
Still another object of the present invention is to provide an image pickup apparatus which can shorten a period of the high-speed sweep operation and can suppress an amount of electric power consumed.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical shift register for receiving signal electric charges of each photoelectric transducer and transferring the signal electric charges in the vertical direction, and a horizontal shift register for transferring the signal electric charges in the vertical shift register in the horizontal direction, and control means for driving and controlling the solid state image pickup device, the control means has a driving function in a mode for sequentially transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, a driving function in a mode for continuously transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register, and an electronic shutter function of extracting accumulated signal electric charges from the photoelectric transducer of the solid state image pickup device to control a photoelectric conversion time, and in an operation using the electronic shutter function, transfer of electric charges in the mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register is performed in the number of times corresponding to the sum of the number of all register units constituting the vertical shift registers and m (m is one or more integer) until the end of the photoelectric conversion time, thereby purging out useless electric charges in the vertical shift registers.
By performing transfer of electric charges in a high-speed sweep mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register in the number of times, mentioned above, for thereby purging out useless electric charges, the high-speed sweep operation can be avoided from being repeated in the number of times larger than required, and the period of the high-speed sweep operation can be cut down. There can be thus provided an image pickup apparatus in which the amount of electric power consumed can be reduced.
Still another object of the present invention is to provide an image pickup apparatus which can suppress variations of an image signal during the period of the high-speed sweep operation.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical shift register for receiving signal electric charges of each photoelectric transducer and transferring the signal electric charges in the vertical direction, and a horizontal shift register for transferring the signal electric charges in the vertical shift register in the horizontal direction, clamp means for clamping an optical black level of the solid state image pickup device, and control means for driving and controlling the solid state image pickup device and for controlling the clamp means, the control means has a driving function in a mode for sequentially transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, and a driving function in a mode for continuously transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register, and when transfer of electric charges in the mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register is performed in the number of times corresponding to at least the number of all register units constituting the vertical shift registers thereby purging out useless electric charges in the vertical shift registers, clamp pulses supplied from the control means to the clamp means are stopped for a period from the time to start purging out the useless electric charges until the transfer of electric charges is ended after being repeated in the number of times corresponding to the sum of the number of all register units constituting the vertical shift registers and m (m is one or more integer).
By stopping the clamp pulses for the period, mentioned above, when transfer of electric charges in a high-speed sweep mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register is performed in the number of times corresponding to at least the number of all register units constituting the vertical shift registers thereby purging out useless electric charges in the vertical shift registers, a CCD signal is not clamped during the period of the high-speed sweep operation, and the useless electric charges purged out by the high-speed sweep operation are prevented from being mixed in optical black areas of the output CCD signal. There can be thus provided an image pickup apparatus in which a stable image signal can be supplied to form a next recording image.
Still another object of the present invention is to provide an image pickup apparatus which can always supply a stable image signal level.
According to the present invention, in an image pickup apparatus comprising a solid state image pickup device made up of a plurality of photoelectric transducers which are two-dimensionally arrayed in the horizontal and vertical directions, a vertical shift register for receiving signal electric charges of each photoelectric transducer and transferring the signal electric charges in the vertical direction, and a horizontal shift register for transferring the signal electric charges in the vertical shift register in the horizontal direction, clamp means for clamping an optical black level of the solid state image pickup device, and control means for driving and controlling the solid state image pickup device and for controlling the clamp means, the control means has a driving function in a mode for sequentially transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register in synchronism with a transfer operation of the horizontal shift register, and a driving function in a mode for continuously transferring the signal electric charges, which have been transferred from the photoelectric transducer of the solid state image pickup device to the vertical shift register, to the horizontal shift register, and when transfer of electric charges in the mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register is performed in the number of times equal to or less than the number of all register units constituting the vertical shift registers thereby purging out useless electric charges in the vertical shift registers, clamp pulses supplied from the control means to the clamp means are stopped for a period given by both the period of purging out the useless electric charge and a number m (m is one or more integer) of horizontal periods after the purge of the useless electric charges.
By stopping the clamp pulses as mentioned above, when an image signal of only necessary lines is to be obtained by performing transfer of electric charges in a high-speed sweep mode for continuously transferring the signal electric charges, which have been transferred to the vertical shift register, to the horizontal shift register in the number, of times equal to or less than the number of all register units constituting the vertical shift registers, the CCD signal can be avoided from being clamped in unstable periods therein. There can be thus provided an image pickup apparatus in which a stable image signal level can be always supplied.